Golf balls having varying numbers of dimples in different arrangements are known. With many of golf balls, the arrangement dimples is determined in the following manner. On a spherical surface externally in contact with a reqular polyhedron, the ridge lines of the polyhedron are projected to obtain lines of projection as phantom lines 2 dividing the spherical surface as seen in FIG. 3. Dimples 1 are formed in an identical arrangement in each of the portions 3 of the spherical surface divided by the phantom dividing lines 2. The regular polyhedron may be a regular octahedron, regular dodecahedron or regular icosahedron, and the corresponding dimple arrangement will hereinafter be referred to as a "regular octahedral arrangement," "regular dodecahedral arrangement" or "regular icosahedral arrangement."
Golf balls heretofore proposed are divided generally into the following five types according to the arrangement pattern and total number of dimples.
A: Golf balls having about 336 dimples 1 in a regular octahedral arrangement as seen in FIG. 3 (showing only the dimples in substantially 1/8 part of the whole area of the spherical surface). PA0 B: Those having about 332 dimples or about 392 dimples generally in an icosahedral arrangement symmetric with respect to the parting line. PA0 C: Those having about 330 to 344 dimples as arranged on concentric circles or in a similar arrangement. PA0 D: Those having 360 dimples in a regular dodecahedral arrangement. PA0 E: Those having 252 dimples in a regular icosahedral arrangement.
Of these, the balls B and C are poor in symmetrical pattern of dimple arrangements because the plane of symmetry containing the center of the ball is limited only to the parting line and thus have some directionality.
The balls A, D and E, each having a regular polyhedral dimple arrangement, are symmetric with respect to planes containing the center of the sphere and the phantom dividing lines 2 and are therefore high in equivalency and superior to the balls B and C.
However, the balls D and E in which the planes of symmetry containing the center of the ball do not intersect one another at right angles are difficult to address, to tee up for making tee shots and to putt along the desired line and accordingly have not been widely accepted.
The ball A having a regular octahedral dimple arrangement is symmetric with respect to planes intersecting one another, is free of the above drawbacks, has been traditionally used and is primarily used at present.
Almost all the balls having this dimple arrangement are provided with 336 dimples although the number of dimples somewhat differs, for example, because the space for the print of brand name has varying sizes.
On the other hand, the golf ball flies at a high speed of 40 to 80 m/sec while rotating also at a high speed of 2000 to 10,000 r.p.m. For the golf ball to achieve an added distance during flying in a low-speed region of its trajectory, i.e. the descending portion thereof from the peak point to the ground, it is required that the change from turbulent air flow separation to laminar air flow separation should take place in a region of the lowest possible speed. The dimples formed in the surface of the ball must fulfill this requirement among other physical functions. In order to maintain the condition of such turbulent air separation as long as possible, it is proposed to lengthen the dimple edge to the greatest possible extent. This can be obtained by giving a larger diameter to the dimples and/or forming an increased number of dimples.
With the ball A having 336 dimples, the above effect can be achieved by increasing the diameter of the dimples. In the case of the dimple arrangement of this ball, the pitch of dimples differs from location to location and is only 3.9 mm when small. Accordingly with small-sized balls having a diameter of 41.15 mm, it is impossible to form too large dimples in view of the number of dimples.